Cellular membranes represent a large store of second messengers that can be enlisted in a variety of signal transduction pathways. In regards function and regulation of effector enzymes in phospholipids signaling pathways, these enzymes generate second messengers from the membrane phospholipid pools (class I PI3 kinases (e.g. PI3Kalpha) are dual-specificity kinase enzymes, meaning they display both: lipid kinase (phosphorylation of phosphoinositides) as well as protein kinase activity, shown to be capable of phosphorylation of protein as substrate, including auto-phosphorylation as intramolecular regulatory mechanism. These enzymes of phospholipids signaling are activated in response to a variety of extra-cellular signals such as growth factors, mitogens, integrins (cell-cell interactions) hormones, cytokines, viruses and neurotransmitters such as described in Scheme I hereinafter and also by intracellular regulation by other signaling molecules (cross-talk, where the original signal can activate some parallel pathways that in a second step transmit signals to PI3Ks by intra-cellular signaling events), such as small GTPases, kinases or phosphatases for example. Intracellular regulation can also occur as a result of aberrant expression or lack of expression of cellular oncogenes or tumor suppressors. The inositol phospholipid (phosphoinositides) intracellular signaling pathways begin with activation of signaling molecules (extra cellular ligands, stimuli, receptor dimerization, transactivation by heterologous receptor (e.g. receptor tyrosine kinase) and the recruitment and activation of PI3K including the involvement of G-protein linked transmembrane receptor integrated into the plasma membrane.
PI3K converts the membrane phospholipid PI(4,5)P2 into PI(3,4,5)P3 that functions as a second messenger. PI and PI(4)P are also substrates of PI3K and can be phosphorylated and converted into PI3P and PI(3,4)P2, respectively. In addition, these phosphoinositides can be converted into other phosphoinositides by 5′-specific and 3′-specific phophatases, thus PI3K enzymatic activity results either directly or indirectly in the generation of two 3′-phosphoinositide subtypes that function as 2nd messengers in intra-cellular signal transduction pathways (Trends Biochem. Sci. 22 (7) p. 267-72 (1997) by Vanhaesebroeck et al.: Chem. Rev. 101 (8) p. 2365-80 (2001) by Leslie et al (2001); Annu. Rev. Cell. Dev. Biol. 17p, 615-75 (2001) by Katso et al. and Cell. Mol. Life. Sci. 59 (5) p. 761-79 (2002) by Toker et al.). Multiple PI3K isoforms categorized by their catalytic subunits, their regulation by corresponding regulatory subunits, expression patterns and signaling-specific functions (p110α, β, δ and γ) perform this enzymatic reaction (Exp. Cell. Res. 25 (1) p. 239-54 (1999) by Vanhaesebroeck and Katso et al., 2001, above).
The closely related isoforms p110α and β are ubiquitously expressed, while δ and γ are more specifically expressed in the haematopoietic cell system, smooth muscle cells, myocytes and endothelial cells (Trends Biochem. Sci. 22 (7) p. 267-72 (1997) by Vanhaesebroeck et al.). Their expression might also be regulated in an inducible manner depending on the cellular, tissue type and stimuli as well as disease context. Inducibility of protein expression includes synthesis of protein as well as protein stabilization that is in part regulated by association with regulatory subunits.
To date, eight mammalian PI3Ks have been identified, divided into three main classes (I, II, and III) on the basis of sequence homology, structure, binding partners, mode of activation, and substrate preference. In vitro, class I PI3Ks can phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PI4P), and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2) to produce phosphatidylinositol-3-phosphate (PI3P), phosphatidylinositol-3,4-bisphosphate (PI(3,4)P2, and phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3, respectively. Class II PI3Ks phosphorylate PI and phosphatidylinositol-4-phosphate. Class III PI3Ks can only phosphorylate PI (Vanhaesebrokeck et al., 1997, above; Vanhaesebroeck et al., 1999, above and Leslie et al, 2001, above)

As illustrated in Scheme A above, phosphoinositide 3-kinases (PI3Ks) phosphorylate the hydroxyl of the third carbon of the inositol ring. The phosphorylation of phosphoinositides that generate PtdIns to 3,4,5-trisphosphate (PtdIns(3,4,5)P3), PtdIns(3,4)P2 and PtdIns(3)P produce second messengers for a variety of signal transduction pathways, including those essential to cell proliferation, cell differentiation, cell growth, cell size, cell survival, apoptosis, adhesion, cell motility, cell migration, chemotaxis, invasion, cytoskeletal rearrangement, cell shape changes, vesicle trafficking and metabolic pathway (Katso et al., 2001, above and Mol. Med. Today 6 (9) p. 347-57 (2000) by Stein). G-protein coupled receptors mediate phosphoinositide 3′OH-kinase activation via small GTPases such as Gβγ and Ras, and consequently PI3K signaling plays a central role in establishing and coordinating cell polarity and dynamic organization of the cytoskeleton—which together provides the driving force of cells to move.
Chemotaxis—the directed movement of cells toward a concentration gradient of chemical attractants, also called chemokines is involved in many important diseases such as inflammation/auto-immunity, neurodegeneration, antiogenesis, invasion/metastasis and wound healing (Immunol. Today 21(6) p. 260-4 (2000) by Wyman et al.; Science 287(5455) p. 1049-53 (2000) by Hirsch et al.; FASEB J. 15(11) p. 2019-21 (2001) by Hirsch et al. and Nat. Immunol. 2(2) p. 108-15 (2001) by Gerard et al.).
Advances using genetic approaches and pharmacological tools have provided insights into signalling and molecular pathways that mediate chemotaxis in response to chemoattractant activated G-protein coupled receptors. PI3-Kinase, responsible for generating these phosphorylated signalling products, was originally identified as an activity associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylates phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al., Trends Cell Biol. 2 p. 358-60 (1992)). However, more recent biochemical studies revealed that class I PI3 kinases (e.g. class IB isoform PI3Kγ) are dual-specific kinase enzymes, meaning they display both lipid kinase and protein kinase activity, shown to be capable of phosphorylation of other proteins as substrates, as well as auto-phosphorylation as an intra-molecular regulatory mechanism.
PI3-kinase activation, is therefore believed to be involved in a range of cellular responses including cell growth, differentiation, and apoptosis (Parker et al., Current Biology, 5 p. 577-99 (1995); Yao et al., Science, 267 p. 2003-05 (1995)). PI3-kinase appears to be involved in a number of aspects of leukocyte activation. A p85-associated PI3-kinase activity has been shown to physically associate with the cytoplasmic domain of CD28, which is an important costimulatory molecule for the activation of T-cells in response to antigen (Pages et al., Nature, 369 p. 327-29 (1994); Rudd, Immunity 4 p. 527-34 (1996)). Activation of T cells through CD28 lowers the threshold for activation by antigen and increases the magnitude and duration of the proliferative response. These effects are linked to increases in the transcription of a number of genes including interleukin-2 (IL2), an important T cell growth factor (Fraser et al., Science 251 p. 313-16 (1991)). Mutation of CD28 such that it can no longer interact with PI3-kinase leads to a failure to initiate IL2 production, suggesting a critical role for PI3-kinase in T cell activation. PI3Kγ has been identified as a mediator of G beta-gamma-dependent regulation of JNK activity, and G beta-gamma are subunits of heterotrimeric G proteins (Lopez-Ilasaca et al., J. Biol. Chem. 273 (5) p. 2505-8 (1998)). Cellular processes in which PI3Ks play an essential role include suppression of apoptosis, reorganization of the actin skeleton, cardiac myocyte growth, glycogen synthase stimulation by insulin, TNFα-mediated neutrophil priming and superoxide generation, and leukocyte migration and adhesion to endothelial cells.
Recently, (Laffargue et al., Immunity 16 (3) p. 441-51 (2002)) it has been described that PI3Kγ relays inflammatory signals through various G(i)-coupled receptors and its central to mast cell function, stimuli in context of leukocytes, immunology includes cytokines, chemokines, adenosines, antibodies, integrins, aggregation factors, growth factors, viruses or hormones for example (J. Cell. Sci. 114(Pt 16) p. 2903-10 (2001) by Lawlor et al.; Laffargue et al., 2002, above and Curr. Opinion Cell Biol. 14(2) p. 203-13 (2002) by Stephens et al.).
Specific inhibitors against individual members of a family of enzymes provide invaluable tools for deciphering functions of each enzyme. Two compounds, LY294002 and wortmannin (cf. hereinafter), have been widely used as PI3-kinase inhibitors. These compounds are non-specific PI3K inhibitors, as they do not distinguish among the four members of Class I PI3-kinases. For example, the IC50 values of wortmannin against each of the various Class I PI3-kinases are in the range of 1-10 nM. Similarly, the IC50 values for LY294002 against each of these PI3-kinases is about 15-20 μM (Fruman et al., Ann. Rev. Biochem., 67, p. 481-507 (1998)), also 5-10 microM on CK2 protein kinase and some inhibitory activity on phospholipases. Wortmannin is a fungal metabolite which irreversibly inhibits PI3K activity by binding covalently to the catalytic domain of this enzyme. Inhibition of PI3K activity by wortmannin eliminates subsequent cellular response to the extracellular factor. For example, neutrophils respond to the chemokine fMet-Leu-Phe (fMLP) by stimulating PI3K and synthesizing PtdIns (3,4,5)P3. This synthesis correlates with activation of the respirators burst involved in neutrophil destruction of invading microorganisms. Treatment of neutrophils with wortmannin prevents the fMLP-induced respiratory burst response (Thelen et al., Proc. Natl. Acad. Sci. USA, 91, p. 4960-64 (1994)). Indeed, these experiments with wortmannin, as well as other experimental evidence, shows that PI3K activity in cells of hematopoietic lineage, particularly neutrophils, monocytes, and other types of leukocytes, is involved in many of the non-memory immune response associated with acute and chronic inflammation.

Based on studies using wortmannin, there is evidence that PI3-kinase function is also required for some aspects of leukocyte signaling through G-protein coupled receptors (Thelen et al., 1994, above). Moreover, it has been shown that wortmannin and LY294002 block neutrophil migration and superoxide release. Cyclooxygenase inhibiting benzofuran derivatives are disclosed by John M. Janusz et al., in J. Med. Chem. 1998; Vol. 41, No. 18.
It is now well understood that deregulation of onocogenes and tumour-suppressor genes contributes to the formation of malignant tumours, for example by way of increase cell growth and proliferation or increased cell survival. It is also now known that signaling pathways mediated by the PI3K family have a central role in a number of cell processes including proliferation and survival, and deregulation of these pathways is a causative factor a wide spectrum of human cancers and other diseases (Katso et al., Annual Rev. Cell Dev. Biol., 2001, 17: 615-617 and Foster et al., J. Cell Science, 2003, 116: 3037-3040).
Class I PI3K is a heterodimer consisting of a p110 catalytic subunit and a regulatory subunit, and the family is further divided into class Ia and Class Ib enzymes on the basis of regulatory partners and mechanism of regulation. Class Ia enzymes consist of three distinct catalytic subunits (p110α, p110β, and p110δ) that dimerise with five distinct regulatory subunits (p85α, p55α, p50α, p85β, and p55γ), with all catalytic subunits being able to interact with all regulatory subunits to form a variety of heterodimers. Class Ia PI3K are generally activated in response to growth factor-stimulation of receptor tyrosine kinases, via interaction of the regulatory subunit SH2 domains with specific phospho-tyrosine residues of the activated receptor or adaptor proteins such as IRS-1. Small GTPases (ras as an example) are also involved in the activation of PI3K in conjunction with receptor tyrosine kinase activation. Both p110α and p110β are constitutively expressed in all cell types, whereas p110δ expression is more restricted to leukocyte populations and some epithelial cells. In contrast, the single Class Ib enzyme consists of a p110γ catalytic subunit that interacts with a p101 regulatory subunit. Furthermore, the Class Ib enzyme is activated in response to G-protein coupled receptor (GPCR) systems and its expression appears to be limited to leukocytes.
There is now considerable evidence indicating that Class Ia PI3K enzymes contribute to tumourigenesis in a wide variety of human cancers, either directly or indirectly (Vivanco and Sawyers, Nature Reviews Cancer, 2002, 2, 489-501). For example, the p110α subunit is amplified in some tumours such as those of the ovary (Shayesteh, et al., Nature Genetics, 1999, 21: 99-102) and cervix (Ma et al., Oncogene, 2000, 19: 2739-2744). More recently, activating mutations within p110α (PIK3CA gene) have been associated with various other tumors such as those of the colon and of the breast and lung (Samuels, et al., Science, 2004, 304, 554). Tumor-related mutations in p85α have also been identified in cancers such as those of the ovary and colon (Philp et al., Cancer Research, 2001, 61, 7426-7429). In addition to direct effects, it is believed that activation of Class Ia PI3K contributes to tumourigenic events that occur upstream in signaling pathways, for example by way of ligand-dependent or ligand-independent activation of receptor tyrosine kinases, GPCR systems or integrins (Vara et al., Cancer Treatment Reviews, 2004, 30, 193-204). Examples of such upstream signaling pathways include over-expression of the receptor tyrosine kinase Erb2 in a variety of tumors leading to activation of PI3K-mediated pathways (Harari et al., Oncogene, 2000, 19, 6102-6114) and over-expression of the oncogene Ras (Kauffmann-Zeh et al., Nature, 1997, 385, 544-548). In addition, Class Ia PI3Ks may contribute indirectly to tumourigenesis caused by various downstream signaling events. For example, loss of function of the PTEN tumor-suppressor phosphatase that catalyses conversion of PI(3,4,5)P3 back to PI(4,5)P2 is associated with a very broad range of tumors via deregulation of PI3K-mediated production of PI(3,4,5)P3 (Simpson and Parsons, Exp. Cell Res., 2001, 264, 29-41). Furthermore, augmentation of the effects of other PI3K-mediated signaling events is believed to contribute to a variety of cancers, for example by activation of AKT (Nicholson and Andeson, Cellular Signaling, 2002, 14, 381-395).
In addition to a role in mediating proliferative and survival signaling in tumor cells, there is also good evidence that class Ia PI3K enzymes also contributes to tumourigenesis via its function in tumor-associated stromal cells. For examples, PI3K signaling is known to play an important role in mediating angiogenic events in endothelial cells in response to pro-angiogenic factors such as VEGF (abid et al., Arterioscler, Thromb. Vasc. Biol., 2004, 24, 294-300). As Class I PI3K enzymes are also involved in motility and migration (Sawyer, Expert Opinion investing. Drugs, 2004, 13, 1-19), PI3K inhibitors are anticipated to provide therapeutic benefit via inhibition of tumor cell invasion and metastasis.